The present disclosure concerns a method for determining a mould shape quality of a user-customized ear mould for an ear piece by means of a mould testing system; the disclosure further concerns a mould testing system for determining a mould shape quality of a user-customized ear mould for an ear piece.
An ear piece is worn in the ear of a user to provide a desired functionality, e.g. hearing aid. The ear piece typically comprises an outer shape or contour designed to fit at least partly into an ear canal. By its outer shape, the ear piece can e.g. be retained in the ear without further support. For some ear pieces it can be desirable that the ear piece acoustically fits into the ear canal, e.g. to block outside noise and/or prevent deterioration of sound generated by the ear piece.
One class of ear pieces has a universal shape that is designed to more or less adapt their shape to the ear of an average individual. Unfortunately, for a universal ear piece, a trade-off is made between the requirement to adapt to different ear shapes by resilient expansion of the outer shape and a comfort level of the user who constantly feels the resilient housing of the ear piece trying to expand inside his ear canal.
Another class of ear pieces are customized to a specific user. The customized ear piece typically comprises a user-customized ear mould with an outer contour moulded to conform with an ear canal of the specific user. An advantage of a user-customized ear piece over a universal ear piece (e.g. “ear buds”), is that an improved sound quality can be achieved at a desired comfort level. One type of customized ear mould comprises an inner passage through the ear mould that is, in use, directed into the ear canal to be in acoustic communication therewith. The inner passage can be fitted with a functional housing, e.g. comprising an acoustic generator, to provide the desired functionality, e.g. hearing aid. Generally, the inner passage of the ear mould has a universal shape such that the functional housing fitted therein can also be universal.
While it is recognized that a proper mould shape quality is important, presently known mould testing systems, e.g. used by audiologists for testing the mould shape of a customized ear mould, have some shortcomings. In particular, the present test system consist of a tube that is connected on one side to the ear mould under test. On the other side, the tube is connected to a pump and a pressure sensor. The shape conformity of the ear mould is tested in situ, i.e. when properly placed in the ear canal. When this is the case, the pump applies a specific over or under pressure to the volume that consists of the tube, the earpiece canal and the cavity in the ear before the tympanic membrane. During pumping the pressure is monitored with the pressure sensor. When the right pressure is reached, the pumping stops. After that the pressure in the volume is monitored during at least five seconds. The worse the shape conformity between the mould and the ear canal is, the faster the pressure will go back to the atmospheric pressure that was in it before. On the other hand, with a perfectly fitting shape the pressure in the volume will stay constant.
When an appropriate pressure is chosen, the method can work. However the pumping makes a lot of noise in the ear. Secondly, either over or under pressure gives an unpleasant feeling, since the tympanic membrane is stretched. Thirdly overpressure tends to push out the ear mould out of the more or less wedge shaped ear canal, which could lead to the unfair judgement that the mould shape does not fit. On the other hand under pressure could lead to sucking in the earpiece, which could lead to the unfair judgement that the mould shape does fit. Finally, the equipment for testing the mould shape as described above is expensive. These and other drawbacks leads to the situation that the mould shape quality is often not tested, whereas this is very important. Especially, because the acoustic fit of a set of customized ear mould will in general be guaranteed for at least two years by the supplier. It is thus highly desirable to determine the mould shape quality when the ear moulds are handed over to the customer in order to have a good starting point.
Accordingly, there is a desire for an improved method for determining mould shape quality of a user-customized ear mould for an ear piece by means of a mould testing system alleviating the above-mentioned shortcomings.